Semiconductor device

ABSTRACT

A substrate voltage control technique that prevents the operating speed from being decreased and suppresses a leakage current due to a lower threshold voltage with respect to a low voltage use. Since a center value of the threshold voltages is detected by plural replica MOS transistors, and a substrate voltage is controlled to control a center value of the threshold voltages, thereby making it possible to satisfy a lower limit of the operating speed and an upper limit of a leakage current of the entire chip. On the other hand, the substrate voltage is dynamically controlled during the operation of the chip, thereby making it possible to decrease the center value of the threshold voltages when the chip operates to improve the speed, and to increase the center value of the threshold voltages after the operation of the chip to reduce the leakage current of the entire chip.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP2006-234896 filed on Aug. 31, 2006, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a semiconductor device, and moreparticularly to a semiconductor memory device that is effective inreducing a variation in a threshold voltage of a sense amplifier of thesemiconductor memory device, and a control method therefor.

BACKGROUND OF THE INVENTION

According to the studies of the present inventors, there have beenproposed the following control technique for the semiconductor device.

For example, dynamic random access memories (hereinafter referred to as“DRAM”) that is one of the semiconductor devices have been incorporatedin large numbers into diverse electronic devices that are used by ususual day. Also, with the low power consumption of the devices and theneeds for the high performance in recent years, the high performancesuch as the lower power, the higher speed, or the higher capacity hasbeen strongly demanded for the incorporated DRAM.

One of the most effective means for realizing the high-performance DRAMis to miniaturize memory cells. The miniaturization makes it possible toreduce the memory cell in sizes. As a result, the respective lengths ofword lines and data lines which are connected to the memory cells areshortened, thereby making it possible to reduce the parasiticcapacitance of the word lines and the data lines. Accordingly, thelow-voltage operation can be conducted, and the low power consumptioncan be realized. Also, since the memory cell is reduced in the size, thecapacity of the memory can be increased, and the higher performance ofthe device can be realized. In this way, the miniaturization greatlycontributes to the higher performance of the DRAM.

However, as the nodes of 65 nm and 45 nm are progressively miniaturized,not only the advantage of the above-mentioned high performance but alsodiverse adverse effects are developed. The main adverse effects are toincrease the variation of the device characteristics which are producedby the miniaturization. In the present specification, the variation inthe device characteristics is directed to, for example, a dispersionvalue (deviation from a mean value) of a threshold voltage of atransistor, or the magnitude of a leakage current that flows from thetransistor. The device variation causes the deterioration in theperformance of the DRAM, it is desirable to suppress the devicevariation as much as possible. In particular, because the thresholdvoltage of the transistor that is used in the sense amplifier greatlyinfluences on the operating speed of the DRAM, and influences the powerconsumption performance when the DRAM stands by, it is stronglydesirable to reduce the variation of the threshold voltage.

In order to reduce the variation in the threshold voltage of thetransistor that is used in the sense amplifier, it is necessary toreduce the manufacturing error in the channel length or the channelwidth. However, a tendency is made to increase the manufacturing erroras the miniaturization is advanced, and it is difficult to reduce themanufacturing error more than that in the conventional art, and toreduce the variation in the threshold voltage. In other words, avariation in the threshold voltage of the cell transistor due to theshort channel effect is increased year by year. When it is assumed thatthe variation in the threshold voltage has a regular distribution, thevariation (a standard deviation α) increases, and when the memorycapacity (population parameter) is increased, the threshold voltage ofthe sense amplifier transistor under the worst conditions is necessarilylowered (or heightened). For that reason, the control for setting thesubstrate voltage deeply (or shallowly) so as to ensure the conditionsof the sense speed and the power consumption is essential even under thecondition of the threshold voltage of the worst sense amplifiertransistor when the threshold voltage that is lowered by the shortchannel effect is assumed.

As the substrate voltage control technique described above, a techniquedisclosed in JP-A No. 2005-86819 has been proposed. JP-A No. 2005-86819discloses a technique by which the substrate voltage of the transistoris controlled to change the threshold voltage in order to hold thecircuit speed constant with respect to the process, the supply voltage,and the temperature variation. The threshold voltage is so changed as toreduce the variation in the threshold voltage and hold the operatingspeed of the transistor constant. Also, in the high-temperature orlow-threshold voltage process condition, the threshold voltage is soincreased as to reduce the leakage current.

SUMMARY OF THE INVENTION

Incidentally, as a result that the present inventors have studied thetechnique of manufacturing the above-mentioned semiconductor device, thepresent inventors have found the following facts.

With the lower power consumption of the DRAM, the lower voltageoperation of the DRAM array has been progressively demanded year byyear. As a result, a voltage that is applied to the bit lines of theDRAM is decreased. In the case where the sense amplifier of the DRAMuses a half pre-charge system, a voltage that is applied to the gates ofan NMOS transistor and a PMOS transistor in the sense amplifier is alsodecreased when amplifying small data that has been stored in the bitline capacitor. As a result, a period of time required when the senseamplifier amplifies the data, and the operation of the DRAM is broken.For that reason, unless the voltage that is applied to the respectiveMOS transistors of the sense amplifier is increased, it is necessarythat the threshold voltage of the MOS transistor is lowered to ensurethe effective voltage that is applied to the gate.

JP-A 2005-86819 discloses a system that controls the threshold voltageof the MOS transistor, and ensures the driving force of the transistor.In order to control the threshold voltage of the MOS transistor, thesystem disclosed in JP-A 2005-86819 monitors the threshold voltage ofone replica MOS transistor, and control the substrate voltage of the MOStransistor on the basis of the monitor result, to thereby control thethreshold voltage. However, in that system, because the number ofreplica MOS transistors is one, there arises such a problem that aprecision of the threshold voltage control is lacked.

More specifically, because a large number of sense amplifier MOStransistors of the DRAM are disposed on the chip, it is impossible tograsp a variation in the threshold voltages of the transistor by onereplica MOS transistor. For that reason, in the case where a transistorthat is very high in the threshold voltage or a transistor that is verylow in the threshold voltage is the replica MOS transistor with respectto a transistor that exists in the center of the threshold voltagedistribution, there is the possibility that the threshold voltage of thesense amplifier MOS transistor is remarkably decreased or remarkablyincreased on the basis of the monitor results. The erroneous thresholdvoltage control induces such problems that the sense speed is decreasedand the power consumption is increased.

Under the above circumstances, the present invention has been made inview of the above problems, and therefore an object of the presentinvention is to provide a control method and a manufacturing method forrealizing a semiconductor device which grasps the distribution of thethreshold voltage of the sense amplifier transistor and controls thesubstrate voltage taking the variation in the threshold voltage intoconsideration so as to suppress the sense speed deterioration and reducethe power consumption.

The above object, other objects, and novel features of the presentinvention will become apparent from the description of the presentspecification and the attached drawings.

The representative outline of the present invention described in thepresent application will be briefly described below.

In the control method for the semiconductor device according to thepresent invention, a large number of replica MOS transistors thatmonitor the threshold voltages of the sense amplifier are disposed on aDRAM chip, and the substrate voltage is determined on the basis of themonitor results including not only the threshold voltages of thetransistors but also a variation in the threshold voltages.

The advantages obtained by the representative features of the presentinvention described in the present application reside in that it ispossible to suppress a decrease in the sense speed or realize the lowerpower consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will becomemore fully apparent from the following detailed description taken withthe accompanying drawings in which:

FIG. 1 is a diagram illustrating an entire NMOS substrate control block;

FIG. 2 is a diagram illustrating an entire PMOS substrate control block;

FIG. 3 is a diagram showing a substrate voltage control circuit;

FIG. 4 is a diagram showing a comparator circuit;

FIG. 5 is a diagram showing a power supply circuit;

FIG. 6 is a diagram showing an entire DRAM chip;

FIG. 7 is a diagram showing a DRAM block;

FIG. 8 is a diagram showing the well configuration of a sense amplifierand a replica MOS transistor;

FIG. 9 is a diagram showing the layout of the sense amplifier;

FIG. 10 is a diagram showing the layout of the replica MOS transistor;

FIG. 11 is a timing chart showing an example of the reading operationwaveforms of a synchronous DRAM to which the present invention isapplied;

FIG. 12 is a timing chart showing an example of the writing operationwaveforms of the synchronous DRAM to which the present invention isapplied;

FIG. 13 is a diagram showing a layout example of a sense amplifier MOStransistor monitoring circuit and a control circuit according to a firstembodiment of the present invention;

FIG. 14 is a diagram showing a layout example of the entire DRAM chip;

FIG. 15 is a diagram showing an entire NMOS threshold voltage variationcontrol block;

FIG. 16 is a diagram showing an entire PMOS threshold voltage variationcontrol block;

FIG. 17 is a diagram showing another layout example of the entire DRAMchip;

FIG. 18 is a diagram showing still another layout example of the entireDRAM chip;

FIG. 19 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 20 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 21 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 22 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 23 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 24 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 25 is a diagram showing yet still another layout example of theentire DRAM chip;

FIG. 26 is a diagram showing yet still another layout example of theentire DRAM chip; and

FIG. 27 is a diagram showing yet still another layout example of theentire DRAM chip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a description will be given in more detail of preferredembodiments of the present invention with reference to the accompanyingdrawings. In all of the drawings for explaining the various embodiments,the same members are indicated by identical references in principle, andtheir duplex description will be omitted.

Also, transistors that constitute the respective blocks shown in therespective embodiments are formed on one semiconductor substrate made ofsingle crystal silicon by an integrated circuit technique of a knownCMOS (complementary MOS transistor) although being not particularlylimited. That is, the transistors are formed by a step of forming firstand second semiconductor regions that constitute a gate electrode and asource/drain region after a step of forming a well, an elementseparation region, and an oxide film.

A circuit symbol of a MOSFET (metal oxide semiconductor field effecttransistor) represents an n-type MOSFET (NMOS) when an arrow is directedoutward with respect to a gate, which is distinguishable over a p-typeMOSFET (PMOS) whose arrow is directed inward with respect to the gate.Hereinafter, the MOSFET is called “MOS” or “MOS transistor” forsimplification.

The present invention is not limited to only a field effect transistorincluding an oxide film that is disposed between a metal gate and asemiconductor layer, but also applied to a circuit using a general FETsuch as an MISFET (metal insulator semiconductor field effecttransistor) including an insulating film therebetween. The MOStransistor includes an MISFET unless otherwise noted.

First Embodiment

Hereinafter, a semiconductor device according to one embodiment of thepresent invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram showing an entire NMOS transistor substratecontrol circuit. The NMOS transistor substrate control circuit isroughly classified into two circuits. One circuit is a sense amplifierNMOS transistor threshold voltage monitoring circuit 101, and anothercircuit is a control circuit 102.

The NMOS transistor threshold voltage monitoring circuit 101 includes areplica NMOS transistor array 103 and a resistor 105. The replica NMOStransistor array 103 is composed of plural replica NMOS transistors 104.All gate terminals of those plural replica NMOS transistors 104 areconnected to a node 111, all drain terminals thereof are connected to anode 112, all source terminals thereof are connected to a node 113, andall substrates are connected to a node 114. The node 111 is input with agate input voltage VGN. The gate input voltage VGN is input with avoltage between a supply voltage (VCC) and a ground voltage. Inparticular, in this embodiment, in order to control the substrate of thesense amplifier NMOS transistor, a bit line precharge voltage (halfvoltage of the bit line voltage) which is a voltage at the time ofstarting the operation of the sense amplifier NMOS transistor is inputas the gate input voltage VGN. The node 113 is connected with a circuitground. The resistor 105 has one end connected to a supply voltage (VCC)and another end connected to the node 112. Also, the node 112 isconnected to an input of the control circuit. The node 114 is connectedto an output of the control circuit. In this specific embodiment, thenumber of replica NMOS transistors is N, and the resistor 105 has such aresistance that the node 112 has substantially the half voltage (½ VCC)of the supply voltage.

The voltage at the node 112 is determined according to the replica NMOStransistor array 103. The respective threshold voltages of the replicaNMOS transistors 104 within the replica NMOS transistor array 103 aredifferent from each other because of the element variation. When thegate input voltage VGN is applied to the node 111, currentscorresponding to the respective threshold voltages flow in therespective replica NMOS transistors. The voltage at the node 112 isdetermined according to the total of currents that flow in therespective replica NMOS transistors. That is, the node 112 has a voltagecorresponding to the center of the threshold voltages of the pluralreplica NMOS transistors 104.

The control circuit 102 compares the voltage at the node 112 with areference voltage, and controls the threshold voltages of the replicaNMOS transistor and the NMOS transistor of the sense amplifier. Thecontrol circuit receives the voltage at the node 112, internallycompares the received voltage with the reference voltage, and determinesthe substrate voltage (node 114) for setting the threshold voltages ofthe replica NMOS transistors and the NMOS transistors of the senseamplifier to output the set substrate voltage. The substrate voltage ofthe replica NMOS transistor changes when the substrate voltage (node114) changes, to thereby change the threshold voltages of the replicaNMOS transistors. As a result the voltage at the node 112 also changes.The control circuit 102 again changes the substrate voltage due to thechanged voltage at the node 112. In this way, the control circuitdetermines an appropriate substrate voltage while gradually changing thesubstrate voltage that is applied to the NMOS transistor.

FIG. 2 is a diagram showing an entire PMOS transistor threshold voltagecontrol block. The PMOS transistor threshold voltage control circuit isroughly classified into two circuits. One circuit is a sense amplifierPMOS transistor threshold voltage monitoring circuit 201, and anothercircuit is a control circuit 202.

The PMOS transistor threshold voltage monitoring circuit 201 is composedof a replica PMOS transistor array 203 and a resistor 205. The replicaPMOS transistor array is composed of plural replica PMOS transistors204. All gate terminals of those plural replica PMOS transistors 204 areconnected to a node 211, all drain terminals thereof are connected to anode 212, all source terminals thereof are connected to a node 213, andall substrates are connected to a node 214. The node 211 is input with agate input voltage VGP. The gate input voltage VGP is input with avoltage between the supply voltage (VCC) and the ground voltage. Inparticular, in this embodiment, in order to control the substrate of thesense amplifier PMOS transistor, the bit line presearch voltage (halfvoltage of the bit line voltage) that is a voltage at the time ofstarting the operation of the sense amplification PMOS transistor isinput as the gate input voltage VGP. That is, in this embodiment, thegate input voltages VGN and VGP can be set to the same voltage, and itis unnecessary to increase the number of power supply circuits. The node213 is connected with the supply voltage (VCC). The resistor 205 has oneend connected to a circuit ground and another end connected to the node212. Also, the node 212 is connected to an input of the control circuit.The node 214 is connected to an output of the control circuit. In thisspecific embodiment, the number of replica PMOS transistors is N, andthe resistor 205 has such a resistance that the node 212 hassubstantially the half voltage (½ VCC) of the supply voltage.

The voltage at the node 212 is determined according to the replica PMOStransistor array 203. The respective threshold voltages of the replicaPMOS transistors 204 within the replica PMOS transistor array 203 aredifferent from each other because of the element variation. When thegate input voltage VGP is applied to the node 211, currentscorresponding to the respective threshold voltages flow in therespective replica PMOS transistors. The voltage at the node 212 isdetermined according to the total of currents that flow in therespective replica PMOS transistors. That is, the node 212 has a voltagecorresponding to the center of the threshold voltages of the pluralreplica PMOS transistors 204.

The control circuit 202 compares the voltage at the node 212 with areference voltage, and controls the threshold voltages of the replicaPMOS transistors and the PMOS transistors of the sense amplifier. Thecontrol circuit receives the voltage at the node 212, internallycompares the received voltage with the reference voltage, and determinesthe substrate voltage (node 214) for setting the threshold voltages ofthe replica PMOS transistors and the PMOS transistors of the senseamplifier to output the set substrate voltage.

FIG. 3 is a diagram showing an internal configuration of the controlcircuit 102 and the control circuit 202. Each of the control circuits isroughly classified into two circuits, that is, a comparator circuitarray 301 and a power supply circuit 302. Plural comparator circuits 303are included in the interior of the comparator circuit array 301. Thecomparator circuit array 301 compares a voltage (monitor output voltage)that is set by the pre-stage sense amplifier NMOS (PMOS) thresholdvoltage monitoring circuit with a reference voltage. The referencevoltage is different in each of the comparator circuits, and has a givenrange of from a lower reference voltage to a higher reference voltage.The respective comparator circuits 303 within the comparator circuitarray 301 compare inputted voltages (monitor output voltage) with thereference voltages, and output the comparison results to the powersupply circuit 302. The power supply circuit 302 outputs the substratevoltage on the basis of the results from the comparator circuit array301.

FIG. 4 is a diagram showing the configuration of the comparators 303within the comparator circuit array 301. Each of the comparator circuits303 is composed of a differential amplifier 401, INV-NOR gates 402, 403,and a flip-flop circuit 404. The comparator circuit 303 compares aninput voltage Iin that is a monitor output voltage with a referencevoltage Vref to determine the substrate voltage. First, the differentialamplifier 401 compares the input voltage Vin with the reference voltageVref, and outputs a high-level signal in the case where the inputvoltage Vin exceeds the reference voltage Vref (node 411). When thehigh-level signal is inputted to an input terminal (node 411) of theINV-NOR gate 402, the high-level signal is inverted into a low-levelsignal by the INV gate 403 and input to the NOR gate 402. In thissituation, in the case where the output node 412 from the comparatorcircuit 303 at the higher voltage side, the output of the INV-NOR gate,that is, the output of the comparator circuit becomes unqualifiedly low.However, in the case where the node 412 is low, the output of theINV-NOR gate, that is, the output of the comparator circuit becomeshigh. Also, in the case where the input voltage Vin is lower than thereference voltage Vref, the low-level signal is outputted (node 411).When the low-level signal is input to the input (node 411) of theINV-NOR gate 402, the low-level signal is inverted into the high-levelsignal by the INV gate 403 and input to the NOR gate. In this situation,the output of the INV-NOR gate, that is, the output of the comparatorcircuit becomes unqualifiedly low regardless of the output node 412 fromthe comparator circuit at the higher voltage side. Also, the flip-flopcircuit 404 takes in and holds the output of the NOR gate at the time ofa change in the clock signal CLK, and outputs the comparison results tothe post-stage power supply circuit 302.

FIG. 5 is a diagram showing the configuration of the internal of thepower supply circuit 302. The power supply circuit 302 is composed ofplural NMOS transistors, and the respective drain terminals of theplural NMOS transistors are set to different voltages. Only onehigh-level signal is outputted from the comparator array 301. The outputis inputted to the gate of the NMOS, and a voltage that is connected tothe drain terminal of the NMOS is outputted as the substrate voltage.

In the case where the substrate voltage is not adjusted by the substratecontrol circuit, the gate input voltage of the replica MOS transistor inthe monitoring circuit is set to the ground voltage in the case of theNMOS and the supply voltage VCC in the case of the PMOS. As a result, anunnecessary DC path can be blocked, and a reduction in the powerconsumption can be realized. However, the nodes 112 and 212 approach thesupply voltage VCC or the ground voltage through the resistor. Under thecircumstances, the operation of the differential amplifier 401 shown inFIG. 3 is stopped, and the substrate voltage to be supplied is heldconstant according to the information that is held by the flip-flopcircuit 404without changing the clock signal CLK. In this way, the powersupply block of the substrate control circuit is realized.

Subsequently, a description will be given of the physical configurationof the semiconductor device according to one embodiment of the presentinvention with reference to FIGS. 6 to 10.

FIG. 6 is a diagram showing the entire chip configuration of the DRAM.The DRAM chip is entirely roughly classified into a control circuit(X/Y-Predec, CLK/Cmd), a memory block 601, and an input/output PAD 602.The control circuit (X/Y-Predec, CLK/Cmd) is inputted with a clocksignal, an address signal, and a control signal from the external of thechip to determine the operating mode of the chip or predecode theaddress. The input/output PAD 602 is inputted with write data, andoutputs read data to the external of the chip. The control circuitincludes an X-decoder X-DEC, a Y-decoder Y-DEC, a predecoder X/Y-Predec,a command decoder CLK/Cmd, a main amplifier MA, and a word driver WD.

The configuration of the memory block 601 is shown in FIG. 7. Pluralmemory cell arrays ARY that are arranged in arrays are disposed in thememory block, and a sense amplifier array SAA, a sub-word driver arraySWDA, and a cross area XP are disposed around the plural memory cellarrays ARY. Also, a replica array replica, a column decoder YDEC, and amain amplifier array MAA are disposed in parallel to the sense amplifierarray in the outer periphery of the block, and a row decoder XDEC isdisposed in parallel to the sub-word driver array. The replica MOStransistors shown in FIGS. 1 and 2 are disposed in the replica arrayreplica.

FIG. 8 shows the memory cell array ARY, the sense amplifier array SAA,and the replica MOS transistor array Replica A. The memory cell array iscomposed of plural memory cells MC. The DRAM cell is composed of one MOStransistor and one capacitor, and one source terminal or drain terminalof the MOS transistor is connected to the bit line, another sourceterminal or drain terminal thereof is connected to a storage node SN,and a gate terminal thereof is connected to a word line. One terminal ofthe capacitor is connected to the storage node SN, and another terminalof the capacitor is connected to the circuit ground.

Plural sense amplifiers SA are disposed in the sense amplifier array,and connected to bit lines of both side arrays. A precharge circuit BLEGequalizes bit lines that are paired when precharge signals BLEQ_U/BLEQ_Dare activated, and precharges the bit lines to a bit line prechargelevel. The bit line precharge level is normally set to a neutral pointVDL/2 of the bit line amplitude VDL (the same level as the supplyvoltage VCC from the external of the chip or a level lower than thesupply voltage VCC). After a minute read signal has been generated fromthe memory cell on the bit line, a cross couple amplifier CCP/CCN drivesthe P-side common source line CSP to the VDL, drives the N-side commonsource line CSN to VSS, and amplifies the higher voltage of the bitlines BLT and BLB to VDL, and the lower voltage to VSS. When a columnselected line YS is activated, local IO lines LIOt/LIOb and a pair ofbit lines are connected to each other. In order to prevent currentconsumption at the non-selected sense amplifier array, LIOt/b isprecharged to the bit line precharge voltage (VBLR) at a standby time.Transistors that are identical in the configuration as the senseamplifier are disposed in parallel to the sense amplifier in the replicaMOS transistor array.

Also, it is necessary to separate P wells PWELL from each other in orderto supply the substrate voltage of the sense amplifier, independently.In this embodiment, although the NMOS cross couple CCN and YSW are ofthe same PWELL, a dummy N well NWELL is disposed between the P wells. Noelement is formed in the N well.

FIG. 9 is a diagram showing a plan layout of the sense amplifier array.Parts of symbols indicative of dashed portions corresponds to therespective circuits that constitute the sense amplifier array SAA-Dshown in FIG. 8, respectively. Also, larger frames indicated by dashedlines represent PWELs and NWELs, respectively. The PWELs are indicatedby the larger dashed lines, and the NWELs are shaded within the largerdashed frame. Reference YS denotes a column switch drive line, and LIOdenotes a local bit line. Also, in FIG. 9, symbol FGCNT denotes a gatecontact that connects the gate electrode and a wiring layer M1 (bitline) of a first layer, LN and LP are diffused layers, FG is a gateelectrode, and LCNT is a diffused layer contact that connects thediffused layers LN, LP and the wiring layer M1. The substrate voltagecontrol conducted in the present invention is to control the voltage ofthe substrate VBBSA_P of the PMOS cross couple (CCP) and the voltage ofthe substrate VBBSA_N of the NMOS cross couple (CCN). That is, thevoltages that are supplied to the substrate VBBSA_P and the substrateVBBSA_N are outputted from the substrate control circuit shown in FIG. 1or 2. The layout diagram of FIG. 9 shows a case in which the substratevoltages (VBBSA_P and VBBSA_N) of the respective cross couples (CCP andCCN) are controlled, independently from other MOS transistors (forexample, SHR or BLEQ). The NMOS cross couples CCN and YSW are of thesame PWELL, and the NWEL is interposed therebetween to separate thoseNMOS cross couples CCN and YSW from each other. With the aboveconfiguration, only the substrate voltage VBBSA_N of the NMOS crosscouple CCN can be controlled, independently. However, the WEL separationallows the layout area to increase. Although being not shown in FIG. 9,unless the WEL separation is conducted, not only the substrate voltageVBBSA_N of the NMOS cross couple CCN, but also the substrate voltages ofthe YSW, SHR, and BLEQ are controlled together. In this case, the layoutarea can be reduced. Also, the PMOS cross couple (CCP) and the NMOScross couple (CCN) which constitute the sense amplifier are constitutedby a so-called ring gate in order to ensure the driving force of the MOStransistor, which is different from other transistors.

FIG. 10 is a diagram showing a plan layout of the replica MOS transistorarray. The configurations of the NMOS transistor and the PMOS transistorare of the same ring gate configuration as that the sense amplifier MOStransistor. As in the circuit configuration shown in FIG. 1, all of thegate terminals of the replica NMOS transistors are connected to M1 so asto connect to the same node, all of the drain terminals are connected toM1 so as to connect to the same node, and all of the source terminalsare connected to M1 so as to connect to the same node. Likewise, all ofthe gate terminals of the replica PMOS transistors are connected to M1so as to connect to the same node, all of the drain terminals areconnected to M1 so as to connect to the same node, and all of the sourceterminals are connected to M1 so as to connect to the same node. Also,in FIG. 10, symbol FGCNT denotes a gate contact that connects the gateelectrode and the wiring layer M1 (bit line) of the first layer, LN andLP are diffused layers, FG is a gate electrode, and LCNT is a diffusedlayer contact LCNT that connects the diffused layers LN, LP and thewiring layer M1. In order to conduct the substrate voltage controlaccording to the present invention, the substrate voltages that are setby the control circuits 102 and 202 are inputted to the VBBSA_N andVBBSA_P from the outputs of the replica NMOS transistor and the replicaPMOS transistor to confirm whether the set substrate voltages aredesired values, or not. In this situation, in the case where additionaladjustment is necessary, the substrate voltages that are set by thecontrol circuits 102 and 202 are inputted to the VBBSA_N and VBBSA_Pfrom the outputs of the replica NMOS transistor and the replica PMOStransistor to determine the results. The above operation is repeated todecide the substrate voltage VBBSA_N of the sense amplifier NMOS crosscouple CCN and the substrate voltage VBBSA_P of the sense amplifier PMOScross couple CCP shown in FIG. 9.

The substrate control operation can be conducted at roughly, forexample, five stages. That is, the five stages consist of (1) a stageimmediately after manufacturing the DRAM chip, (2) a stage when a poweris supplied to the DRAM chip, (3) a stage when a mode register is set,(4) a stage when the mode transits to a test mode where the substratecontrol operation is conducted, and (5) a stage of the normal operation.

First, a description will be given of a case in which the substratecontrol operation is conducted immediately after manufacturing the DRAMchip of (1). The substrate control circuit operates to adjust thesubstrate voltage at the time of conducting a text immediately aftermanufacturing the DRAM chip. In the case where the substrate controloperation is conducted immediately after manufacturing, it is necessaryto store the adjusted result in a nonvolatile memory. Accordingly, it isnecessary that the selector circuit 106 or 206 shown in FIG. 1 or 2selects a fixed voltage by the aid of a known fuse or nonvolatilememory, and also the result when the reset signal RST is inputted to theflip-flop 404 shown in FIG. 4 is inputted.

Subsequently, a description will be given of a case in which a power issupplied to the DRAM chip not immediately after manufacturing the DRAMchip. In the case where the substrate control operation is conductedafter the power is supplied to the DRAM chip, (2) a stage immediatelyafter the power is supplied, (3) a stage when the mode register is set,and (4) a stage when the mode transits to the test mode are represented.In the case of (2) to (4), that one of (2) to (4) is selectivelyexecuted is enough, but as the occasion demands, the combination of (2)to (4) can be executed in plural times without any problem. Also, theadjustment period can be measured by a timer, or can be set to “sincepower supply till mode register setting” or “since mode register settingtill an initial access”. The importance is that it is necessary toensure a sufficient time in order to adjust the substrate voltage. Afterthe adjustment, the clock signal CLK shown in FIG. 4 is stopped, theinformation is held in the flip-flop circuit 404, the fixed voltage isselected by the selector circuit 106 or 206 shown in FIG. 1 or 2, andthe operation of the monitoring circuit is stopped.

Also, it is possible to conduct the dynamic control in the normaloperation. In the case of conducting the dynamic control, it isdetermined whether it is before or after the operation of the senseamplifier. In the case where it is before the sense amplifier operation,the substrate voltage is set to be shallower, and the threshold voltagesof the NMOS and PMOS transistors of the sense amplifier are set to belower, to thereby increase the sense speed. On the other hand, in thecase where it is after the sense amplifier operation, the substratevoltage is set to be deeper, and the threshold voltage of the NMOStransistor of the sense amplifier is set to be higher, to thereby reducethe power consumption.

The memory array operation will be described with reference to FIG. 11.FIG. 11 is a timing chart showing an example of the reading operationwaveforms of the semiconductor device to which the present invention isapplied. When an active command ACT is inputted together with a lowaddress, the address is decoded internally. As a result, in the senseamplifier block of the corresponding address, the bit line prechargesignals BLEQ_U and BLEQ_D transit to a deactivated state. In thisexample, because the precharge circuit BLEQ is configured by NMOS, thebit line precharge signals transit from the higher voltage level of theactivated state, for example, from a word line step-up power supply VWHor a bit lien amplitude voltage VDL to a ground level VSS. As a result,the precharge of the bit line of the corresponding memory cello array isstopped. Then, the word lien WL corresponding to the input address isselected. In this situation, as the selected word line, one word linethat is connected to one memory cell, for example, WL1 of FIG. 8 isactivated. Then, the activated word line WL1 transits from a word linestandby level to a word line select level VWH. With this operation, inthe memory cell MC, the gate of the transistor is selected, a storagenode SN and the bit line are connected to each other, and the data inthe memory cell is read by the bit line. This example shows a case inwhich data of “H” is saved in the memory cell storage node SN. In thissituation, the bit line becomes higher in voltage as large as electriccharges that have been stored in the storage node SN than the prechargelevel. In this situation, the NMOS sense amplifier activated signal NCStransits from the ground level VSS of the non-selected state to thehigher voltage VDL of the activated state, or the word line voltage VWHa given period of time after the word line has been activated, tothereby activate the NMOS cross couple. Substantially at the same time,or late, the PMOS sense amplifier activated signal PCS transits from thehigher voltage state VDL of the non-selected state or the word linevoltage VWH to the ground level VSS of the activated state to activatethe PMOS cross couple. As a result, a minute signal voltage that isdeveloped in the bit line is amplified up to the bit line amplitudevoltage. This state is a column command input waiting state. An actualcolumn command can be input simultaneously when or before the bit lineamplitude becomes sufficient. This example shows that a read commandREAD is inputted from the external. A column address to be read at thesame time as the read command READ is inputted. Upon inputting the readcommand, the column select line YS transits from the ground level VSS ofthe standby state to the bit line amplitude voltage VDL of the selectstate from the column decoder to come to an activated state according tothe address that has been input at the same time. As a result, the datathat has been held in the sense amplifier is read to the input/outputline LIOt/b. Thereafter, although being not shown, the data is outputtedto the external through the main amplifier and the input/output section.Subsequently, the operation when the precharge command PRE is inputtedwill be described. When the precharge command is inputted, the selectedword line transits to the word line waiting level VWL in a state wherethe selected word line is non-selected. With the above operation, thesense amplifier activated signals NCS and PCS are unselected. After thesense amplifiers have been deactivated, the bit line precharge signalsBLEQ_U and BLEG_D are activated, and all of the bit lines and thereference bit lines of the activated memory cell array AARY are set tothe bit line precharge level. In this drawing, the bit line prechargelevel is set to VDL/2 that is ½ of the bit line amplitude voltage. Withthis operation, the precharging operation is completed.

Subsequently, the writing operation will be described with reference toFIG. 12. Upon inputting the active command ACT, the sense amplifier isactivated, and the same reading operation as that described above isconducted until the column command is inputted. The writing operation isconducted by inputting a write command WRIT and a write address in acolumn command input waiting state at the same time. That is, there area case in which the write command WRIT and the write address areinputted immediately after the active command as shown in FIG. 12, orinput after the above-mentioned read command READ. The write data isinputted together with the command and the address, or at the leading ortrailing edge of a clock after one clock cycle time. The write data isinputted from an input/output pin DQ, and then transferred to aninternal input/output line LIOt/b. The transferred data is written inthe sense amplifier circuit that is connected to the write cell by theaid of a column selected line YS that is selected according to the writeaddress which has been input together with the write command. In thesense amplifier, the bit line is driven according to the data that hasbeen written from the input/output line LIOt/b to write data in thestorage node of the memory cell. FIG. 12 shows a waveform diagram inwhich “H” data is written in the cell where the read data is “L”. Theinternal operation after the precharge command has been input is thesame as that described in the above-mentioned reading operation. Thisoperation is described as one of the operation of DDRSDRAM, but thesubstrate voltage control according to the present invention can beapplied to the normal SDRAM or a DDR2-SDRAM.

FIG. 13 shows a block diagram when the layout of the sense amplifier MOStransistor threshold voltage monitoring circuit shown in FIG. 10 isactually arranged with respect to the layout of the sense amplifiershown in FIG. 9. The control unit shown in the block diagram is madeadaptive to the half bank and one bank. The sense amplifier MOStransistor threshold voltage monitoring circuit is arranged in parallelto the sense amplifiers between the Y-decoder (Y-DEC) and the senseamplifier arrays 141 (SA). As described above, the sense amplifier MOStransistor threshold voltage monitoring circuit has the sameconfiguration as that of the sense amplifier MOS transistor. The abovearrangement makes it possible to monitor a variation in the thresholdvoltage of the sense amplifier MOS transistor of the sense amplifierarrays 141 with high precision, and to control the substrate voltage soas not to suffer from a problem on the variation in the thresholdvoltage of the sense amplifiers on both sides of the sense amplifierarrays 141.

FIG. 17 shows a block diagram of a semiconductor device according toanother embodiment of the present invention. This embodiment changes thelayout of the sense amplifier MOS transistor threshold voltagemonitoring circuit shown in FIG. 13. A difference in the layout betweenFIGS. 17 and 13 resides in that the sense amplifier MOS transistorthreshold voltage monitoring circuit is arranged between the X-decoder(X-DEC) and array blocks 181 so that the longitudinal positions of thesense amplifiers and the monitoring circuit are equal to each other. Asdescribed above, the sense amplifier MOS transistor threshold voltagemonitoring circuit has the same configuration as that of the senseamplifier MOS transistor. The above arrangement makes it possible tomonitor a variation in the sense amplifier MOS transistor thresholdvoltage of the sense amplifiers and the array blocks 181 with highprecision, and to detect the threshold voltage center value includingthe variation in the sense amplifier threshold voltage on both of theupper and lower ends and control the substrate voltage.

FIG. 18 is a block diagram showing a semiconductor device according tostill another embodiment of the present invention. A difference of FIG.18 from FIGS. 13 and 17 resides in that two sense amplifier MOStransistor threshold voltage monitoring circuits are arranged. One senseamplifier MOS transistor threshold voltage monitoring circuit isarranged between the Y-decoder (Y-DEC) and the sense amplifier arrays191 (SA) so as to be in parallel to the sense amplifiers, and anothersense amplifier MOS transistor threshold voltage monitoring circuit isarranged between the X-decoder (X-DEC) and the array block 192 so thatthe longitudinal positions of the sense amplifiers and the monitoringcircuit are equal to each other. As described above, the sense amplifierMOS transistor threshold voltage monitoring circuits have the sameconfiguration as that of the sense amplifier MOS transistor. The abovearrangement makes it possible to monitor a variation in the thresholdvoltages of the lateral sense amplifier MOS transistors of the senseamplifier arrays 191 and a variation in the threshold voltages of thelongitudinal sense amplifier MOS transistors within the sense amplifierand array blocks 192 with high precision. With the above configuration,not only a variation in the threshold voltage of the MOS transistors inone direction of the lateral direction or the longitudinal direction,but also a variation in the threshold voltage of the MOS transistorsthat are physically farthest from each other can be monitored. Also, itis possible to detect the center value of the threshold voltagesincluding the threshold voltage variations of the sense amplifiers thatare physically disposed at the farthest ends from each other, andcontrol the substrate voltage.

FIG. 19 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 18 resides in that three sense amplifier MOS transistor thresholdvoltage monitoring circuits are disposed. A first sense amplifier MOStransistor threshold voltage monitoring circuit is disposed between theY-decoder (Y-DEC) and the sense amplifier arrays 201 (SA) so as to be inparallel to the sense amplifiers. A second sense amplifier MOStransistor threshold voltage monitoring circuit is disposed between theX-decoder (X-DEC) and an array block 202, and a third sense amplifierMOS transistor threshold voltage monitoring circuit is disposed at aright side of an array block 203, in such a manner that the longitudinalpositions of the sense amplifiers and the monitoring circuits are equalto each other, respectively. As described above, the sense amplifier MOStransistor threshold voltage monitoring circuits have the sameconfiguration as that of the sense amplifier MOS transistor. The abovearrangement makes it possible to monitor a variation in the thresholdvoltages of the lateral sense amplifier MOS transistors of the senseamplifier arrays 201 and a variation in the threshold voltages of thelongitudinal sense amplifier MOS transistors within the sense amplifierand arrayblocks 202 and 203 with high precision. With the aboveconfiguration, not only a variation in the threshold voltage of the MOStransistors in one direction of the lateral direction or thelongitudinal direction, but also a variation in the threshold voltage ofthe MOS transistors that are physically farthest from each other as wellas a variation in the threshold voltage which is different between bothof right and left ends of the MOS transistors in the same longitudinaldirection can be monitored. It is possible to detect the center value ofthe threshold voltages including a variation in the threshold voltage inthe lateral direction in the vicinity of the Y-DEC and a variation inthe threshold voltage which is different between both of right and leftends in the same longitudinal direction, and control the substratevoltage.

FIG. 20 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 19 resides in that four sense amplifier MOS transistor thresholdvoltage monitoring circuits are disposed. A first sense amplifier MOStransistor threshold voltage monitoring circuit is disposed between theY-decoder (Y-DEC) and sense amplifier arrays 211 (SA) so as to be inparallel to the sense amplifiers. A second sense amplifier MOStransistor threshold voltage monitoring circuit is disposed at an upperside of sense amplifier arrays 213 (SA) so as to be in parallel to thesense amplifiers. A third sense amplifier MOS transistor thresholdvoltage monitoring circuit is disposed between the X-decoder (X-DEC) andan array block 212, and a fourth sense amplifier MOS transistorthreshold voltage monitoring circuit is disposed at a right side of anarray block 213 in such a manner that the longitudinal positions of thesense amplifiers and the monitoring circuits are equal to each other,respectively. As described above, the sense amplifier MOS transistorthreshold voltage monitoring circuits have the same configuration asthat of the sense amplifier MOS transistor. The above arrangement makesit possible to monitor a variation in the threshold voltages of thelateral sense amplifier MOS transistors of the sense amplifier arrays211 and 213, and a variation in the threshold voltages of thelongitudinal sense amplifier MOS transistors within the sense amplifierand array blocks 202 and 203 with high precision. With the aboveconfiguration, not only a variation in the threshold voltage of the MOStransistors in one direction of the lateral direction or thelongitudinal direction, but also a variation in the threshold voltagewhich is different between both of upper and lower ends of the MOStransistors even in the same lateral direction, as well as a variationin the threshold voltage which is different between both of right andleft ends of the MOS transistors even in the same longitudinal directioncan be monitored. From the above monitoring results, it is possible todetect the center value of the threshold voltages including a variationin the threshold voltage which is different between both of upper andlower ends even in the lateral direction and a variation in thethreshold voltage which is different between both of right and left endseven in the same longitudinal direction, and control the substratevoltage.

FIG. 21 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 13 resides in that the array block is divided into two parts fromthe center, and the sense amplifier MOS transistor threshold voltagemonitoring circuits and the control circuits are disposed in the upperand lower portions, independently. One sense amplifier MOS transistorthreshold voltage monitoring circuit is disposed between the Y-decoder(Y-DEC) and a sense amplifier array 221 (SA) so as to be in parallel tothe sense amplifiers, and another sense amplifier MOS transistorthreshold voltage monitoring circuit is disposed at an upper side of asense amplifier array 222 (SA) so as to be in parallel to the senseamplifiers. As described above, the sense amplifier MOS transistorthreshold voltage monitoring circuits have the same configuration asthat of the sense amplifier MOS transistor. Since the sense amplifierMOS transistor threshold voltage monitoring circuits and the controlcircuits are provided in the upper half and the lower half, separately,it is possible to more finely detect the center value of the thresholdvoltages including a variation in the threshold voltages of the lateralsense amplifier MOS transistors, and to more finely control thesubstrate voltage as compared with a case in which only one controlcircuit is provided.

FIG. 22 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 21 resides in that the layout of the sense amplifier MOS transistorthreshold voltage monitoring circuits is changed. The upper monitoringcircuit and the lower monitoring circuit are disposed in parallel to theX-DEC in such a manner that the longitudinal positions of the senseamplifier MOS transistors of an array block 231 and the MOS transistorsof the monitoring circuit are equal to each other. As described above,the sense amplifier MOS transistor threshold voltage monitoring circuitshave the same configuration as that of the sense amplifier MOStransistor. Since the sense amplifier MOS transistor threshold voltagemonitoring circuits and the control circuits are provided in the upperhalf and the lower half, separately, it is possible to more finelydetect the center value of the threshold voltages including a variationin the threshold voltages of the longitudinal sense amplifier MOStransistors, and to more finely control the substrate voltage ascompared with a case in which only one control circuit is provided.

FIG. 23 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference betweenFIGS. 21 and 22 resides in that the layout of the sense amplifier MOStransistor threshold voltage monitoring circuits is changed. One senseamplifier MOS transistor threshold voltage monitoring circuit isdisposed between the Y-DEC and a sense amplifier array 241 so as to bein parallel to the sense amplifiers, and another sense amplifier MOStransistor threshold voltage monitoring circuit is disposed at an upperside of a sense amplifier array 242 so as to be in parallel to the senseamplifiers. In the longitudinal direction, an upper monitoring circuitand a lower monitoring circuit are arranged in parallel to the X-DEC insuch a manner that the longitudinal positions of the sense amplifier MOStransistor of the array block 243 and the MOS transistor of themonitoring circuit are equal to each other. As described above, thesense amplifier MOS transistor threshold voltage monitoring circuitshave the same configuration as that of the sense amplifier MOStransistor. Since the sense amplifier MOS transistor threshold voltagemonitoring circuits and the control circuits are provided in the upperhalf and the lower half, separately, it is possible to more finelydetect the center value of the threshold voltages including a variationin the threshold voltages of the lateral sense amplifier MOS transistorsand a variation in the threshold voltages of the longitudinal senseamplifier MOS transistors, and to more finely control the substratevoltage as compared with a case in which only one control circuit isprovided.

FIG. 24 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 23 resides in that the layout of the sense amplifier MOS transistorthreshold voltage monitoring circuits is changed. One sense amplifierMOS transistor threshold voltage monitoring circuit is disposed betweenthe Y-DEC and a sense amplifier array 251 so as to be in parallel to thesense amplifiers, and another sense amplifier MOS transistor thresholdvoltage monitoring circuit is disposed at an upper side of a senseamplifier array 252 so as to be in parallel to the sense amplifiers. Inthe longitudinal direction, an upper monitoring circuit and a lowermonitoring circuit are arranged at both of the right and left sides inparallel to the X-DEC in such a manner that the longitudinal positionsof the sense amplifier MOS transistors of the array blocks 253 and 254and the MOS transistors of the monitoring circuit are equal to eachother. As described above, the sense amplifier MOS transistor thresholdvoltage monitoring circuits have the same configuration as that of thesense amplifier MOS transistor. Since the sense amplifier MOS transistorthreshold voltage monitoring circuits and the control circuits areprovided in the upper half and the lower half, separately, it ispossible to more finely detect the center value of the thresholdvoltages including a variation in the threshold voltage of the lateralsense amplifier MOS transistors and a variation in the threshold voltageof the longitudinal sense amplifier MOS transistors, and to more finelycontrol the substrate voltage as compared with a case in which only onecontrol circuit is provided.

FIG. 25 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 13 resides in that the layout of the sense amplifier MOS transistorthreshold voltage monitoring circuits is changed. A sense amplifier MOStransistor threshold voltage monitoring circuit is disposed in thecenter of a block in parallel to the Y-DEC. As described above, thesense amplifier MOS transistor threshold voltage monitoring circuit hasthe same configuration as that of the sense amplifier MOS transistor.Since the sense amplifier MOS transistor threshold voltage monitoringcircuit is disposed in the center of the block, it is possible tomonitor the more actual threshold voltage of the sense amplifier MOStransistor with high precision as compared with a case in which thesense amplifier MOS transistor threshold voltage monitoring circuit isdisposed out of the block as shown in FIG. 24 and other above-mentionedfigures. As a result, it is possible to enhance a precision in thedetection of the center value of the threshold voltages, and control thesubstrate voltage on the basis of the center value of the thresholdvoltages.

FIG. 26 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 25 resides in that the layout of the sense amplifier MOS transistorthreshold voltage monitoring circuits is changed. The sense amplifierMOS transistor threshold voltage monitoring circuits are disposed inparallel to the Y-DEC, so as to be in the center of the block, betweenthe Y-DEC and a sense amplifier array 271, and at an upper side of thesense amplifier array 272, respectively. As described above, the senseamplifier MOS transistor threshold voltage monitoring circuits have thesame configuration as that of the sense amplifier MOS transistor. Thesense amplifier MOS transistor threshold voltage monitoring circuits aredisposed in the center of the block; at the upper side, and at the lowerside, respectively, so as to increase the number of monitors, therebymaking it possible to enhance a precision in the detection of the centervalue of the threshold voltage, and to control the substrate voltage onthe basis of the center value of the threshold voltages.

FIG. 27 shows a block diagram of a semiconductor device according to yetstill another embodiment of the present invention. A difference fromFIG. 26 resides in that the layout of the sense amplifier MOS transistorthreshold voltage monitoring circuits is changed. The sense amplifierMOS transistor threshold voltage monitoring circuits are disposed inparallel to the Y-DEC, so as to be in the center of the block, betweenthe Y-DEC and the sense amplifier array 271, and at an upper side of thesense amplifier array 272, respectively. Also, the sense amplifier MOStransistor threshold voltage monitoring circuits are disposed betweenthe X-DEC and an array block 283. As described above, the senseamplifier MOS transistor threshold voltage monitoring circuits have thesame configuration as that of the sense amplifier MOS transistor. Thesense amplifier MOS transistor threshold voltage monitoring circuits aredisposed in the center of the block, at the upper side, at the lowerside, and at the side, respectively, so as to increase the number ofmonitors, thereby making it possible to enhance a precision in thedetection of the center value of the threshold voltage as compared withFIG. 26, and to control the substrate voltage on the basis of the centervalue of the threshold voltages.

Second Embodiment

FIG. 14 is a diagram showing the entire block of a semiconductor deviceaccording to another embodiment of the present invention. A differencefrom the first embodiment resides in that variation control circuits 153and 154 are added. The variation control circuits detect variations inthe threshold voltages of the sense amplifier NMOS/PMOS transistorswithin the chip according to the outputs from the entire NMOS (PMOS)substrate control blocks (sense amplifier NMOS/PMOS transistor thresholdvoltage monitoring circuits 151 and the control circuits 152) shown inFIGS. 1 and 2, which are disposed in plurality within the DRAM chip, andcontrol the substrate voltage of the entire chip to control thethreshold voltages. As a result, it is possible to adjust the sensespeed at an optimum speed, and it is possible to reduce the powerconsumption. The sense amplifier NMOS/PMOS transistor threshold voltagemonitoring circuit 151 shown in FIG. 14 which will be described later issubstantially identical with that shown in FIGS. 1 and 2. Also, thecontrol circuit 152 are substantially identical with that shown in FIGS.1 and 2.

FIG. 15 is a diagram showing the entire block of the NMOS thresholdvoltage variation control circuit 153. A difference from the NMOStransistor substrate control circuit shown in FIG. 1 resides in that theoutputs from the NMOS substrate control circuits within the DRAM chipshown in FIG. 1 are inputted to substrates 1621, 1622, 1623, . . . N ofthe NMOS transistors. With the above configuration, because a voltage ata node 1612 is determined according to an NMOS transistor array 1603, itis possible to adjust a variation in the entire DRAM chip. In thisembodiment, the substrate voltage of the sense amplifier is suppliedfrom not the substrate control circuit shown in FIG. 1 but the thresholdvoltage variation control circuit 153 shown in this figure.

FIG. 16 is a diagram showing the entire block of the PMOS thresholdvoltage variation control circuit 154. A difference from the PMOStransistor substrate control circuit shown in FIG. 2 resides in that theoutputs from the entire PMOS substrate control block within the DRAMchip are inputted to substrates 1721, 1722, 1723, . . . N of the PMOStransistors. Because a voltage at a node 1712 is determined according toa PMOS transistor array 1703, it is possible to adjust a variation inthe entire DRAM chip. In this embodiment, the substrate voltage of thesense amplifier is supplied from not the substrate control circuit shownin FIG. 1 but the threshold voltage variation control circuit 153 shownin this figure.

As a result, the threshold voltages that satisfy both of thespecifications of the sense speed and the power consumption can be setfrom the variations of the center values of the respective thresholdvoltages which are detected by the NMOS/PMOS substrate control blocksthat are located in each of the banks or each of the half banks withinthe DRAM chip by controlling the substrate voltage.

The operation flow in this embodiment is classified into three phases. Afirst phase is a threshold voltage center value detection phase due tothe NMOS/PMOS substrate control block. In the phase, the thresholdvoltage center value is detected in each of the separated regions (eachof banks, each of half banks) within the chip. A second phase is a phasein which the substrate voltage of the sense amplifier NMOS/PMOStransistors of the entire DRAM chip is determined according to theNMOS/PMOS threshold voltage variation control blocks. In the phase, thethreshold voltages that are varied in each of the locations of the DRAMchip are determined so as to satisfy the specifications of the sensespeed and the power consumption. A third phase is a phase in which thesubstrate voltage that is determined according to the NMOS/PMOSthreshold voltage variation control block is inputted to the NMOS/PMOStransistors of all the sense amplifiers within the DRAM chip to controlthe threshold voltage. As a result, it is possible to realize the senseamplifier that satisfies the specifications of the sense speed and thepower consumption. Unless a desired threshold voltage can be set at onetime, the first phase to the third phase are severally repeated tocontrol the threshold voltages.

The present invention described in the present invention and thedrawings have been described with reference to the diverse embodiments.However, the present invention can be diversely modified withoutdeviating from the sprit of the invention.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and modifications and variations are possible in lightof the above teachings or may be acquired from practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and its practical application to enableone skilled in the art to utilize the invention in various embodimentsand with various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto, and their equivalents.

1. A semiconductor device comprising: a plurality of first MOStransistors of a first conductivity type; a first monitoring circuithaving a plurality of first replica MOS transistors of the firstconductivity type; and a first control circuit controlling a substratevoltage of the plurality of first MOS transistors, wherein the firstmonitoring circuit detects a center value of threshold voltages of theplurality of first replica MOS transistors, and outputs a detectionresult to the first control circuit, and wherein the first controlcircuit outputs the substrate voltages of the plurality of first MOStransistors in order to control the threshold voltages of the pluralityof first MOS transistors based on the detection result.
 2. Thesemiconductor device according to claim 1 including a plurality of eachof said first monitoring and first control circuit.
 3. The semiconductordevice according to claim 1, wherein the first control circuit includesa plurality of comparator circuits that compare an output of the firstmonitoring circuit with a reference voltage.
 4. The semiconductor deviceaccording to claim 3, wherein the first control circuit includes a powersupply circuit that determines the substrate voltages of the pluralityof first replica MOS transistors or the plurality of first MOStransistors based on an output from the plurality of comparatorcircuits.
 5. The semiconductor device according to claim 1, wherein theplurality of first replica MOS transistors and the first control circuitare disposed at a periphery of a memory array block.
 6. Thesemiconductor device according to claim 1, wherein the plurality offirst replica MOS transistors and the first control circuit are disposedwithin a memory array block.
 7. The semiconductor device according toclaim 1, further comprising: a plurality of second MOS transistors of asecond conductivity type that is different from the first conductivitytype; a second monitoring circuit having a plurality of second replicaMOS transistors of the second conductivity type; and a second controlcircuit that controls the substrate voltages of the plurality of secondMOS transistors, wherein the second monitoring circuit detects a centervalue of threshold voltages of the plurality of second replica MOStransistors , and outputs a detection result to the second controlcircuit, and wherein the second control circuit outputs the substratevoltages of the plurality of second MOS transistors in order to controlthe threshold voltages of the plurality of second MOS transistors basedon the detection result.
 8. The semiconductor device according to claim7 including a plurality of each of said second monitoring and secondcontrol circuits disposed on a semiconductor integrated circuit chip. 9.The semiconductor device according to claim 8, wherein a variation inthe threshold voltages of the plurality of second MOS transistors isdetected by the plurality of second replica MOS transistors and theplurality of second control circuits.
 10. The semiconductor deviceaccording to claim 1, wherein the plurality of first MOS transistorsconstitute elements of sense amplifiers.
 11. A semiconductor devicecomprising: a plurality of first MOS transistors of a first conductivitytype; a first MOS transistor substrate control circuit including a firstmonitoring circuit having a plurality of first replica MOS transistorsof the first conductivity type, and a first control circuit thatcontrols substrate voltages of the plurality of first replica MOStransistors; and a second MOS transistor substrate control circuitincluding a second monitoring circuit having a plurality of secondreplica MOS transistors of the first conductivity type, and a secondcontrol circuit that controls substrate voltages of the plurality offirst MOS transistors, wherein the first monitoring circuit detects acenter value of threshold voltages of the plurality of first replica MOStransistors and outputs a detection result to the first control circuit,wherein the first control circuit outputs the substrate voltage of eachfirst replica MOS transistor to a corresponding one of the secondreplica MOS transistors in order to control the threshold voltages ofthe plurality of first replica MOS transistors based on the detectionresult, and wherein the second control circuit controls the substratevoltages of the plurality of first MOS transistors based on an output ofthe second monitoring circuit.
 12. The semiconductor device according toclaim 11 including a plurality of first MOS transistor substrate controlcircuits, wherein the second MOS transistor substrate control circuit isdisposed in a center of a chip.
 13. The semiconductor device accordingto claim 11, wherein the first control circuit includes a plurality ofcomparator circuits that compare the output of the first monitoringcircuit with a first reference voltage, and wherein the second controlcircuit includes a plurality of comparator circuits that compare theoutput of the second monitoring circuit with a second reference voltage.14. The semiconductor device according to claim 12, wherein theplurality of first replica MOS transistors and the first control circuitof each of the plurality of first MOS transistor substrate controlcircuits are disposed at a periphery of a memory array block.
 15. Thesemiconductor device according to claim 12, wherein the plurality offirst replica MOS transistors and the first control circuit of each ofthe plurality of first MOS transistor substrate control circuits aredisposed within a memory array block.